Mobile terminals, such as smartphones and tablet terminals, are increasingly being used, whereby applications used in the mobile terminals have diversified. The increased use of the mobile terminals and the diversification have led to a huge communication traffic load and a sharp increase in the number of accesses.
Some of the applications, such as video streaming, involve particularly high traffic. Furthermore, some of the applications, such as chatting and Voice over IP, involve relatively low traffic and a large number of accesses. The increase in the use of the former applications has raised a problem of increased traffic. Furthermore, recently, the use of the latter applications has increased, and thus now there is also a problem of a huge number of accesses. All things considered, a serious problem, which is congestion in a wireless network, is caused by the increased traffic and the huge number of accesses.
As one solution to the problem described above, a hierarchical cell structure (also known as a hierarchical network, and hereinafter referred to as “HCS” in the present application) have been under study. The HCS is a wireless network structure as a combination of a macrocell base station (hereinafter, simply referred to as “macrocell”) that covers a wide area and a microcell base station (hereinafter, simply referred to as “microcell”) that covers a smaller area. In the present application, the microcell is a term used for all the cells relatively small with respect to the macrocell. Thus, the microcell includes a femtocell, a picocell, and the like.
A standardizing body 3GPP (3rd Generation Partnership Project) has standardized the HCS of a wireless network based on LTE (Long Term Evolution) or LTE-Advanced (hereinafter, referred to as “LTE-A”) as the successor of the LTE. The HCS is known as HetNet (Heterogeneous Network).
The HCS, which was originally a technique for increasing area coverage in a wireless network, has recently been used for preventing the congestion in a wireless network. For example, in the HetNet, the microcell is disposed at a local place (hot spot), such as a coffee shop or a school involving high traffic, in an area of a macrocell network. Thus, the local high traffic can be covered by the microcell covering a smaller area, whereby congestion due to high traffic in particular can be prevented.